CN109254358B

CN109254358B - Coherent optical receiver module and method of manufacturing the same

Info

Publication number: CN109254358B
Application number: CN201810756345.8A
Authority: CN
Inventors: 黑川宗高; 藤村康
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 2017-07-14
Filing date: 2018-07-11
Publication date: 2022-06-28
Anticipated expiration: 2038-07-11
Also published as: JP2019020571A; US10209422B2; US20190018179A1; JP6922501B2; CN109254358A

Abstract

The invention discloses a coherent optical receiver module and a manufacturing method thereof. The module includes a housing, a fiber set, a first optical element, and a second optical element. The housing houses a first optical member disposed on an optical path of the local oscillation beam and a second optical member disposed on an optical path of the signal beam. The optical fiber set includes a first optical fiber optically coupled with the first optical component and a second optical fiber optically coupled with the second optical component. The first optical element has a first lens disposed on an optical path of the local oscillation light beam and transmitting the signal light beam and the local oscillation light beam. The second optical element has a second lens that is disposed on an optical path of the signal beam and transmits the signal beam and the local oscillation beam. The first optical element and the second optical element are positioned side-by-side between the group of optical fibers and one end surface of the housing.

Description

Coherent optical receiver module and method of manufacturing the same

Technical Field

The invention relates to a coherent optical receiver module and a method of manufacturing the same.

Background

Japanese patent publication No. jp-2014-187506A discloses an optical receiver module for coherent optical communication. The housing of the module is provided with connectors placed side by side, which are connected to a Single Mode Fiber (SMF) for introducing the signal beam and a Polarization Maintaining Fiber (PMF) for introducing the local oscillator beam, respectively.

Disclosure of Invention

An aspect of the present invention relates to a coherent optical receiver module for demodulating information included in a phase-modulated signal beam by interfering a local oscillation beam with the phase-modulated signal beam. The coherent optical receiver module includes: the optical fiber module comprises a shell, an optical fiber group, a first optical element and a second optical element. The housing has an end surface intersecting the first direction. The housing accommodates a first optical member disposed on an optical path of the local oscillation beam and a second optical member disposed on an optical path of the signal beam. The fiber group is arranged with the facing end surface. The optical fiber group includes a first optical fiber optically coupled to the first optical component to propagate the local oscillator beam and a second optical fiber optically coupled to the second optical component to propagate the signal beam. The first optical element has a first lens disposed on an optical path of the local oscillation beam output from the first optical fiber. The first optical element is configured to transmit a signal beam and a local oscillator beam therethrough. The second optical element has a second lens arranged on an optical path of the signal beam output from the second optical fiber. The second optical element is configured to transmit the signal beam and the local oscillator beam therethrough. The first optical element and the second optical element are positioned side by side along a first direction between the optical fiber group and one end surface.

Drawings

The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

fig. 1 is a partial sectional view showing the configuration of a coherent optical receiver module of an embodiment;

fig. 2 is a sectional view showing an optical plug and a coupling portion;

fig. 3 is a diagram showing the configuration of a first optical element and a second optical element;

fig. 4 is a front view showing the first lens holder;

fig. 5 is a side view showing the first lens holder;

fig. 6 is a front view showing the second lens holder;

fig. 7 is a side view showing the second lens holder;

fig. 8 is a side view showing a state where the first lens holder, the second lens holder, the coupling sleeve, and the alignment sleeve are assembled together and the second lens holder is engaged with one end surface;

FIG. 9 is an example of a flow chart illustrating a method of manufacturing a coherent optical receiver module;

FIG. 10 is a diagram illustrating a manufacturing process of a coherent optical receiver module;

FIG. 11 is a diagram illustrating a manufacturing process of a coherent optical receiver module;

FIG. 12 is a diagram illustrating a manufacturing process of a coherent optical receiver module;

Fig. 13 is a schematic diagram showing a configuration of a coherent optical receiver module as a comparative example;

fig. 14 is a front view showing a first lens holder of a modification;

fig. 15 is a side view showing a first lens holder of a modification;

fig. 16 is a front view showing a second lens holder of a modification;

fig. 17 is a side view showing a second lens holder of a modification; and is

Fig. 18 is a side view showing a state in which the first lens holder of the modification, the second lens holder of the modification, the coupling sleeve, and the alignment sleeve are assembled together and the second lens holder is engaged with one end surface.

Detailed Description

[ problems to be solved by the invention ]

The optical receiver module disclosed in JP2014-187506 is provided with two lenses inside a connector (optical input port) connected to two optical fibers (i.e., SMF and PMF). The two lenses optically couple the signal beam output from the SMF and the local oscillator beam output from the PMF to respective optical components in the housing. In recent years, there has been a demand for miniaturization of an optical receiver module for coherent optical communication. The above-described structure provided with two lenses for two optical fibers, respectively, hinders downsizing of the optical receiver module due to the outer dimension of each optical input port. Therefore, it is conceivable to place two lenses as one lens array at one optical input port and two optical fibers as an optical fiber array corresponding to the lens array.

However, this structure may deviate the intervals between the optical axes of the respective lenses of the lens array and the intervals between the cores of the respective optical fibers of the optical fiber array from each other due to, for example, manufacturing variability. Such deviation may reduce the coupling efficiency between the signal and/or local oscillator beams passing through the respective lenses and the optical components in the housing. In addition, if two lenses are integrated into a lens array, the positions of the lenses cannot be individually adjusted when manufacturing the light receiver module, and thus it is difficult to precisely align each lens. It is conceivable to pull the optical fiber inside the housing, but such a structure may result in reduced productivity and may be more expensive because special handling of the optical fiber is required.

[ Effect of the present disclosure ]

According to the coherent optical receiver module and the manufacturing method thereof of the present disclosure, the size of the coherent optical receiver module can be reduced while reducing the decrease in optical coupling efficiency.

[ description of embodiments of the invention ]

First, the contents of the embodiments of the present invention will be listed and described. A module according to one embodiment of the present invention is a coherent optical receiver module for demodulating information contained in a signal beam by interfering a local oscillator beam with the signal beam that has been phase-modulated. The coherent optical receiver module includes: the optical fiber module comprises a shell, an optical fiber group, a first optical element and a second optical element. The housing has an end surface intersecting the first direction. Accomodate in the casing: a first optical member arranged on an optical path of the local oscillation beam; and a second optical member disposed on an optical path of the signal beam. The optical fiber group is arranged with the facing end surface. The optical fiber group includes: a first optical fiber optically coupled to the first optical component to propagate the local oscillator beam; and a second optical fiber optically coupled to the second optical component to propagate the signal beam. The first optical element has a first lens disposed on an optical path of the local oscillation beam output from the first optical fiber. The first optical element is configured to transmit a signal beam and a local oscillator beam therethrough. The second optical element has a second lens arranged on an optical path of the signal beam output from the second optical fiber. The second optical element is configured to transmit the signal beam and the local oscillator beam therethrough. The first optical element and the second optical element are positioned side by side along a first direction between the optical fiber group and one end surface.

In the coherent optical receiver module, a first optical element having a first lens arranged on an optical path of a local oscillation light beam and a second optical element having a second lens arranged on an optical path of a signal light beam are arranged side by side along a first direction, the first optical element transmits the signal light beam and the local oscillation light beam, and the second optical element transmits the signal light beam and the local oscillation light beam. Therefore, the interval between the optical axis of the first lens and the optical axis of the second lens can be narrowed, and one optical coupling system including the first lens and the second lens for the optical fiber group can be constituted. In other words, the first and second lenses may be housed in a single optical input port. As a result, the coherent optical receiver module can be miniaturized. In addition, the first lens and the second lens are provided in the first optical element and the second optical element, respectively. Accordingly, the first lens and the second lens may be aligned separately when manufacturing the coherent optical receiver module. As a result, a decrease in optical coupling efficiency between the first optical fiber and the first optical member and a decrease in optical coupling efficiency between the second optical fiber and the second optical member can be reduced.

The first and second lenses may be arranged such that optical axes of the first and second lenses are offset from centers of the first and second optical elements. A first region of the first optical element opposite to the first lens with respect to a center of the first optical element may have no lens and may be located on an extension of an optical axis of the second lens. A second region of the second optical element opposite to the second lens with respect to a center of the second optical element may have no lens and may be located on an extension of an optical axis of the first lens. Accordingly, the alignment of the first lens can be performed without being affected by the position of the second optical element, and the alignment of the second lens can be performed without being affected by the position of the first optical element. Therefore, a decrease in optical coupling efficiency between the first optical fiber and the first optical member and a decrease in optical coupling efficiency between the second optical fiber and the second optical member can be further reduced. The first region in the first optical element may define a planar region and may be located on an extension of an optical axis of the second lens. The second region in the second optical element may define a planar region and may be located on an extension of an optical axis of the first lens.

The first optical element may be located between the group of optical fibers and the second optical element in the first direction.

The second lens may include a meniscus lens (meniscus lens). Therefore, even if the distance between the second lens and the optical fiber group is longer than the distance between the first lens and the optical fiber group in the first direction, the size of the beam diameter of the signal beam transmitted through the second lens can be made close to the size of the beam diameter of the local oscillation beam transmitted through the first lens. As a result, the decrease in the optical coupling efficiency between the second optical fiber and the second optical member can be further reduced. The second optical element may include a surface facing the end surface of the housing, and the surface of the second optical element may be provided with a concave surface of the second lens.

The coherent optical receiver module may further include a first holder that holds the first optical element and a second holder that holds the second optical element. The housing may include a bushing disposed adjacent to a sidewall of the housing having a window (window), and the bushing may be provided with an end surface. The first holder may have a first positioning portion on the outer periphery, the second holder may have a second positioning portion on the outer periphery, and the bush may have a third positioning portion on the outer periphery. The first, second, and third positioning portions may be aligned on a line parallel to the first direction.

The first holder may comprise a cut-out or an indication plane on the outer circumference and the second holder may comprise a cut-out or an indication plane on the outer circumference. The cut-out or index plane of the first holder may be aligned with the cut-out or index plane of the second holder. The housing may include a bushing disposed adjacent to a sidewall of the housing having the window. The bushing may be provided with an end surface and the bushing may comprise a cut-out or an indicating plane on the outer circumference. The cut-out or indicating plane of the first holder, the cut-out or indicating plane of the second holder and the cut-out or indicating plane of the bush may be aligned on a line parallel to the first direction.

A method according to one embodiment of the invention is a method of manufacturing a coherent optical receiver module. The method comprises the following steps: a step of preparing (prepare) a housing having one end surface, an optical fiber group including a first optical fiber configured to propagate a local oscillator beam and a second optical fiber configured to propagate a signal beam, a first optical element having a first lens, and a second optical element having a second lens; a step of positioning a first optical element between an end surface of the housing and the optical fiber group to align a first lens of the first optical element with an optical axis of the first optical fiber; a step of fixing the first optical element to the optical fiber group; a step of positioning a second optical element between the end surface and the first optical element to align a second lens of the second optical element with an optical axis of the second optical fiber; and a step of fixing the second optical element to the first optical element and the end surface of the housing.

In manufacturing the above-described coherent optical receiver module, the second lens may be aligned after aligning the first lens and fixing the position of the first optical element. The reason is as follows. In aligning the first lens, it may be necessary to rotate the fiber set about the central axis to adjust the polarization direction of the local oscillator beam. If the second lens is first aligned and fixed to the optical fiber group, when the optical fiber group is rotated about the central axis to align the first lens next, the position of the second lens may move about the central axis with the rotation. As a result, the position of the optical axis of the aligned second lens may deviate. Thus, positioning the first optical element between the optical fiber group and the second optical element makes it possible to align the first lens first and reduce deviation of the position of the optical axis of the second lens due to the influence of the alignment of the first lens. As a result, the decrease in the optical coupling efficiency between the second optical fiber and the second optical member can be further reduced.

In the above method, in the preparing step (the step of preparing the housing, the optical fiber group, the first optical element, and the second optical element), the first holder holding the first optical element therein may be prepared together with the first optical element, and the second holder holding the second optical element therein may be prepared together with the second optical element. The housing may be provided with a bush adjacent a side wall of the housing, and the first and second holders and the bush may each have a cut-out or an indication plane. In the step of positioning the first optical element, the cutout or the indicating plane of the first holder may be aligned with the cutout or the indicating plane of the bush, and in the step of positioning the second optical element, the cutout or the indicating plane of the second holder may be aligned with the cutout or the indicating plane of the bush.

[ details of embodiments of the invention ]

Next, some embodiments of a coherent optical receiver module and a method of manufacturing the same according to the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to those embodiments, but has a scope defined in the claims, and includes all changes, modifications, and equivalents that come within the scope of the claims. In the description of the drawings, the same or similar numerals or symbols denote the same or similar elements to each other without overlapping the explanation.

Fig. 1 is a partial sectional view showing the configuration of a coherent optical receiver module 1 (hereinafter referred to as "optical receiver module 1") according to one embodiment of the present invention. Fig. 2 is a sectional view showing the optical plug 20 and the coupling section 10. For ease of understanding, an XYZ orthogonal coordinate system is shown in each drawing. In fig. 1, the connection relationship of optical components inside the optical receiver module 1 is schematically shown. In fig. 1 and 2, the coupling portion 10 and the optical plug 20 are shown in an XZ sectional view. The optical receiver module 1 causes the local oscillation light beam L2 to interfere with the received phase-modulated signal light beam L1, thereby demodulating the information included in the signal light beam L1. The optical receiver module 1 converts the demodulated information into an electric signal and outputs the electric signal to the outside of the module 1.

As shown in fig. 1, the optical receiver module 1 includes a housing 2 of a substantially rectangular parallelepiped shape, a coupling portion 10 fixed to the housing 2, and an optical plug 20 connected to the coupling portion 10. The housing 2 may be made of Kovar (Kovar), for example. The housing 2 has four side walls. The bush 2b having the Z axis as a central axis is located on a side wall having a window among four side walls of the housing 2. The bush 2b has one end surface 2a intersecting the Z direction. In other words, the one end surface 2a is provided on the bush 2 b. The bush 2b protrudes from the side wall having the window toward the outside of the housing 2. A V-shaped notch 2c extending in the Z direction is formed on the outer peripheral surface of the bush 2 b. In short, the V-shaped notch 2c is provided on the outer periphery of the bush 2 b. A V-shaped notch 2c is provided at one end of the bush 2b in the Y direction. A plurality of lead terminals 3 are disposed on at least one side wall of the case 2 other than the side wall having the window. A plurality of lead terminals 3 are led out from the lowermost layer of the multilayer ceramic constituting each side wall of the case 2. The plurality of lead terminals 3 include a terminal for extracting an electric signal generated from the signal light beam L1 to the outside of the optical receiver module 1, a terminal for supplying a bias voltage to an electronic circuit inside the housing 2, a ground terminal, and the like.

The optical plug 20 extends in the Z direction and is arranged to face one end surface 2a of the bush 2 b. The optical plug 20 has an optical fiber unit 21, a ferrule 24, and a capillary tube (ferrule) 25. The optical fiber unit 21 includes a Single Mode Fiber (SMF)22 and a Polarization Maintaining Fiber (PMF) 23. The SMF 22 and PMF 23 extend in the Z direction and are placed side by side in the X direction. SMF 22 propagates signal beam L1 and outputs signal beam L1 to coupling section 10. The PMF 23 propagates the local oscillation light beam L2 and outputs a local oscillation light beam L2 to the coupling section 10. The signal light beam L1 and the local oscillation light beam L2 are input into the housing 2 through the coupling section 10. The ferrule 24 has a cylindrical shape with the Z direction as the center axis direction. The ferrule 24 receives an end of each of the SMF 22 and PMF 23. The capillary 25 is inserted into the ferrule 24 and holds the ends of the SMF 22 and PMF 23.

The coupling portion 10 has a cylindrical shape extending in the Z direction. One end of the coupling portion 10 in the Z direction is engaged with one end surface 2a of the bush 2 b. The other end of the coupling portion 10 is connected to the optical plug 20. The coupling portion 10 has a first optical element 11, a second optical element 12, a first lens holder 14, a second lens holder 15, a coupling sleeve 16 and an alignment sleeve 17. Each of the first optical element 11 and the second optical element 12 has a columnar shape with the central axis of the ferrule 24 as its central axis. The first optical element 11 and the second optical element 12 are placed side by side in the Z direction between the one end surface 2a of the bush 2b and the optical fiber unit 21.

The first optical element 11 is disposed between the optical fiber unit 21 and the second optical element 12 in the Z direction, and is arranged on the optical path of the signal light beam L1 output from the SMF 22 and the optical path of the local oscillation light beam L2 output from the PMF 23. The first optical element 11 transmits the signal light beam L1 and the local oscillation light beam L2. The first optical element 11 has a first lens 11a located on the optical path of the local oscillation light beam L2, a front end face 11b facing the optical fiber unit 21, and a rear end face 11c located at a position opposite to the front end face 11b (see fig. 2). The first lens 11a is a convex lens located on the front end face 11 b. The first lens 11a converts the local oscillation light beam L2 into collimated light.

The second optical element 12 is disposed between the first optical element 11 and the bush 2b in the Z direction, and is arranged on the optical path of the signal light beam L1 output from the SMF 22 and the optical path of the local oscillation light beam L2 output from the PMF 23. The second optical element 12 transmits the signal beam L1 and the local oscillation beam L2. The second optical element 12 has a second lens 12a located on the optical path of the signal light beam L1, a front end surface 12b facing the rear end surface 11c, and a rear end surface 12c located opposite to the front end surface 12b (see fig. 2). The second lens 12a may be a meniscus lens including a convex surface formed on the front end surface 12b and a concave surface formed on the rear end surface 12 c. The second lens 12a converts the signal light beam L1 into collimated light.

The configuration of the first optical element 11 and the second optical element 12 will be described in more detail.

Fig. 3 is a diagram showing the configuration of the first optical element 11 and the second optical element 12. Fig. 3 shows the focal point f1 of the first lens 11a and the focal point f2 of the second lens 12 a. The focal point f1 coincides with (i.e., coincides with) the position at which the signal light beam L1 is output from the SMF 22, and the focal point f2 coincides with the position at which the local oscillator light beam L2 is output from the PMF 23. As shown in fig. 3, the optical axis a1 of the first lens 11a is located at a position deviated from the center C1 of the first optical element 11. More specifically, the optical axis a1 is positioned in the lens region 11d on one side in the X direction with respect to the center C1 of the first optical element 11, and is located on the extension line of the optical axis of the PMF 23. The planar area 11e on the other side of the first optical element 11 (i.e., the side opposite to the optical axis a1 with respect to the center C1 of the first optical element 11) has no lens and is located on the extension of the optical axis of the SMF 22.

The optical axis a2 of the second lens 12a is located at a position deviated from the center C2 of the second optical element 12. More specifically, the optical axis a2 is positioned in the lens region 12d on the other side in the X direction with respect to the center C2 of the second optical element 12, and is located on the extension line of the optical axis of the SMF 22. The plane area 11e of the first optical element 11 is located on an extension of the optical axis a 2. The lens region 12d is located at a position facing the planar region 11e of the first optical element 11 in the Z direction. The plane area 12e on the side of the second optical element 12 (i.e., the side opposite to the optical axis a2 with respect to the center C2 of the second optical element 12) has no lens and is located on the extension of the axis a1 of the first lens 11 a. The plane area 12e is located at a position facing the lens area 11d of the first optical element 11 in the Z direction.

Here, the movement of the signal light beam L1 output from the SMF 22 and the movement of the local oscillation light beam L2 output from the PMF 23 will be described. The signal light beam L1 output from the SMF 22 passes through the planar region 11e of the first optical element 11 while propagating, and then passes through the second lens 12a of the second optical element 12. At this time, the second lens 12a converts the signal light beam L1 into collimated light. Then, the signal light beam L1 converted into collimated light is input into the housing 2. On the other hand, the local oscillation light beam L2 output from the PMF 23 passes through the first lens 11 a. At this time, the first lens 11a converts the local oscillation light beam L2 into collimated light. Then, the local oscillation light beam L2 passes through the plane area 12e of the second optical element 12 while maintaining the state of collimated light, and is input into the housing 2.

As shown in fig. 1 and 2, the first lens holder 14 is located between the optical plug 20 and the bush 2b in the Z direction, and holds or houses the first optical element 11 in the first lens holder 14. The first lens holder 14 has a cylindrical shape with the center axis of the ferrule 24 as its center axis. As shown in fig. 2, the first lens holder 14 includes a rear end 14a and a front end 14b opposite to each other in the Z direction, a thick cylinder 14c located adjacent to the front end 14b side in the Z direction, and a thin cylinder 14e other than the thick cylinder 14 c. The front end 14b faces the ferrule 24 in the Z direction. The outer diameter of the thick cylinder 14c is substantially equal to the outer diameter of the liner 2 b. The outer diameter of the thin cylinder 14e is smaller than that of the thick cylinder 14 c. The first optical element 11 is inserted into the thin cylinder 14 e. The inner diameter of the thin cylinder 14e is equal to or slightly larger than the outer diameter of the first optical element 11.

Fig. 4 is a front view showing the first lens holder 14. Fig. 5 is a side view showing the first lens holder 14. Fig. 4 is a diagram of the first lens holder 14 shown in fig. 1 when viewed from the Z direction, and fig. 5 is a diagram of the first lens holder 14 shown in fig. 1 when viewed from the Y direction. As shown in fig. 4 and 5, the thick cylinder 14c includes a V-shaped notch 14d extending in the Z direction. A V-shaped notch 14d is formed at the outer periphery of the thick cylinder 14c, and is provided at one end of the thick cylinder 14c in the Y direction. The relative angle of the first optical element 11 with respect to the first lens holder 14 about its central axis is defined with reference to the position of the V-shaped cut 14 d. Thereby, the relative position of the first lens 11a with respect to the first lens holder 14 is defined.

As shown in fig. 1 and 2, the second lens holder 15 is located between the first lens holder 14 and the bush 2b in the Z direction, and holds or houses the second optical element 12 in the second lens holder 15. The second lens holder 15 has a cylindrical shape with the central axis of the ferrule 24 as its central axis. As shown in fig. 2, the second lens holder 15 includes a rear end 15a and a front end 15b opposite to each other in the Z direction, a thick cylinder 15c located adjacent to the front end 15b in the Z direction, and a thin cylinder 15e other than the thick cylinder 15 c. The rear end 15a engages with the bush 2b (see fig. 1). The front end 15b faces the rear end 14a in the Z direction. The outer diameter of the thick cylinder 15c is substantially equal to the outer diameter of the thick cylinder 14c of the first lens holder 14. The outer diameter of the thin cylinder 15e is smaller than that of the thick cylinder 15 c. The second optical element 12 is inserted into the thick cylinder 15 c. The inner diameter of the thick cylinder 15c is equal to or slightly larger than the outer diameter of the second optical element 12.

Fig. 6 is a front view showing the second lens holder 15. Fig. 7 is a side view showing the second lens holder 15. Fig. 6 is a diagram of the second lens holder 15 shown in fig. 1 when viewed from the Z direction, and fig. 7 is a diagram of the second lens holder 15 shown in fig. 1 when viewed from the Y direction. As shown in fig. 6 and 7, the thick cylinder 15c includes a V-shaped notch 15d extending in the Z direction. A V-shaped notch 15d is formed in the outer periphery of the thick cylinder 15c and provided at one end of the thick cylinder 15c in the Y direction. The relative angle of the second optical element 12 about its central axis with respect to the second lens holder 15 is defined with reference to the position of the V-shaped cut 15 d. Thereby, the relative position of the second lens 12a with respect to the second lens holder 15 is defined.

Reference is again made to fig. 1 and 2. Each of the coupling sleeve 16 and the alignment sleeve 17 has a cylindrical shape with the central axis of the ferrule 24 as its central axis. One end of the coupling sleeve 16 in the Z direction is engaged with the front end 15b of the second lens holder 15. The other end of the coupling sleeve 16 faces the thick cylinder 14c of the first lens holder 14 in the Z direction. The thin tube 14e of the first lens holder 14 is inserted into the coupling sleeve 16. Coupling sleeve 16 has an inner diameter equal to or slightly larger than the outer diameter of barrel 14 e. The coupling sleeve 16 has an outer diameter smaller than that of the thick cylinder 15 c. The distance in the Z direction between the first lens holder 14 and the second lens holder 15 is defined by fixing the coupling sleeve 16 and the thin cylinder 14e to each other by welding, for example, at a predetermined position in the Z direction. Thereby, the distance in the Z-direction between the first optical element 11 and the second optical element 12 is defined.

One end of the alignment sleeve 17 in the Z direction is engaged with the front end 14b of the first lens holder 14. The ferrule 24 is inserted into the alignment sleeve 17. The inner diameter of the alignment sleeve 17 is equal to or slightly larger than the outer diameter of the ferrule 24. The outer diameter of the alignment sleeve 17 is smaller than the outer diameter of the thick cylinder 14c of the first lens holder 14 and the outer diameter of the thick cylinder 15c of the second lens holder 15. The alignment sleeve 17 holds the optical fiber unit 21 together with the ferrule 24 and the capillary 25. The distance between the first lens holder 14 and the ferrule 24 in the Z direction is defined by fixing the alignment sleeve 17 and the ferrule 24 to each other by welding, for example, at a predetermined position in the Z direction. As a result, the distance between the first optical element 11 and the optical fiber unit 21 in the Z direction is defined.

Fig. 8 is a side view showing a state where the first lens holder 14, the second lens holder 15, the coupling sleeve 16, and the alignment sleeve 17 are assembled together, and the rear end 15a of the second lens holder 15 is engaged with the bush 2 b. Fig. 8 is a side view when viewed from the Y direction. As shown in fig. 8, the V-shaped

notches

14d and 15d are located at the same positions as the V-shaped notches 2c formed on the outer peripheral surface of the bush 2b when viewed from the Z direction. In other words, the V-shaped notch 14d, the V-shaped notch 15d, and the V-shaped notch 2c are located on a line parallel to the Z direction. The shape of the V-shaped notch 14d and the shape of the V-shaped notch 15d coincide with the shape of the V-shaped notch 2c in the circumferential direction. By arranging the position in the circumferential direction of the V-shaped cutout 14d of the first lens holder 14 to coincide with the position in the circumferential direction of the V-shaped cutout 2c of the bush 2b, the relative angle of the first lens holder 14 with respect to the bush 2b about the central axis thereof is defined. Thereby, the relative position of the first lens 11a with respect to the bushing 2b is defined. Further, by arranging the position in the circumferential direction of the V-shaped cutout 15d of the second lens holder 15 to coincide with the position in the circumferential direction of the V-shaped cutout 2c of the bush 2b, the relative angle of the second lens holder 15 with respect to the bush 2b about the central axis thereof is defined. Thereby, the relative position of the second lens 12a with respect to the bushing 2b is defined.

Reference is again made to fig. 1. In addition to the above-described configuration, the optical receiver module 1 of the present embodiment houses optical hybrids (optical hybrids) 30 and 31 in the housing 2, the

optical hybrids

30 and 31 causing the signal light beam L1 and the local oscillation light beam L2 to interfere with each other. The

light mixers

30 and 31 may be, for example, light 90 ° mixing elements. The

light mixers

30 and 31 are placed side by side in the X direction in the housing 2. The optical receiver module 1 houses in the housing 2: a Polarization Beam Splitter (PBS) 32; a skew adjuster 33; two

lenses

34 and 35; a half-wave (λ/2) plate 36; and a mirror 37 as a first optical component for optically coupling the SMF 22 to each signal beam input point of the

optical hybrid

30, 31.

The PBS 32 is located on the optical path of the signal light beam L1 output from the SMF 22. The PBS 32 has a light incident surface optically coupled with the SMF 22, and splits the signal light beam L1 into one polarization component (for example, an X polarization component that is a component included in the XZ plane) L11 and another polarization component (for example, a Y polarization component that is a component included in the YZ plane) L12. In this case, the beam splitting ratio is, for example, 50%. One polarization component L11 passes directly through the PBS 32 and travels toward the signal beam input point of the optical hybrid 30. The traveling direction of the other polarization component L12 is changed by 90 ° by the PBS 32, and the other polarization component L12 travels toward the mirror 37.

The skew adjuster 33 and the lens 34 are located on an optical path between the PBS 32 and the signal-beam input point of the optical mixer 30 (i.e., on an extension of the optical axis of the signal-beam input point of the optical mixer 30). The one polarization component L11 that has passed through PBS 32 passes through skew adjuster 33. The skew adjuster 33 is, for example, a block member made of Si, and equivalently extends the optical path length of the one polarization component L11 to compensate for the phase delay of the other polarization component L12 with respect to the one polarization component L11 due to the difference between the optical path lengths of the other polarization component L12 and the one polarization component L11. After passing through the skew adjuster 33, the one polarization component L11 is converged by the lens 34 to the signal beam input point of the optical hybrid 30. The traveling direction of the other polarization component L12 split by the PBS 32 is changed by 90 ° again by the mirror 37, and then the other polarization component L12 travels toward the signal beam input point of the optical hybrid 31.

The half-wave plate 36 and the lens 35 are located on the optical path between the mirror 37 and the signal beam input point of the optical hybrid 31. The other polarization component L12 reflected by mirror 37 passes through half-wave plate 36. The half-wave plate 36 rotates the polarization direction of the further polarization component L12 by 90 °. Thus, the polarization direction of the other polarization component L12 that has passed through half-wave plate 36 coincides with the polarization direction of one polarization component L11 that has passed directly through PBS 32. The other polarization component L12 passes through the PBS 32 and is then converged by the lens 35 to the signal beam input point of the light mixer 31.

The optical receiver module 1 further houses in the housing 2: a skew adjuster 33, a mirror 37, a polarizer 38, a Beam Splitter (BS)39, and two

lenses

40 and 41 as second optical components for optically coupling the PMF 23 to each signal beam input point of the

optical mixers

30, 31. The polarizer 38 is optically coupled to the PMF 23 and is located on the optical path of the local oscillation light beam L2 output from the PMF 23. The polarizer 38 adjusts the polarization direction of the local oscillation light beam L2. Thus, even if the polarization direction held in the PMF 23 is deviated when the housing 2 is assembled, only the polarization component having the polarization direction of 0 ° or 90 ° can be extracted as the local oscillation light beam L2. When the light source of the local oscillation light beam L2 is a semiconductor LD, the local oscillation light beam L2 is generally elliptically polarized light in which the polarization component parallel to the active layer is dominant. However, there are cases where distortion due to lattice mismatch is introduced into the active layer to obtain oscillation stability, material reliability, a desired output wavelength, and the like of the semiconductor LD. The laser beam output from such a semiconductor LD may be elliptically polarized light having a longer minor axis length. Even in this case, the polarizer 38 converts the local oscillation light beam L2 from elliptically polarized light into linearly polarized light having a desired polarization direction (for example, a direction included in the XZ plane).

The BS 39 splits the local oscillation light beam L2 output from the polarizer 38 into two parts. The beam splitting ratio is 50: 50. one of the split local oscillation light beams L21 passes directly through the BS 39 and travels toward the local oscillation light beam input point of the optical hybrid 30. The traveling direction of the other local oscillation light beam L22 is changed by 90 ° by the BS 39, and then the other local oscillation light beam L22 travels toward the reflection mirror 37. The skew adjuster 33 and the lens 40 are located on the optical path between the BS 39 and the local oscillation beam input point of the optical mixer 30 (i.e., on the extension of the optical axis of the local oscillation beam input point of the optical mixer 30). The local oscillator light beam L21 traveling directly through the BS 39 passes through the skew adjuster 33. The skew adjuster 33 equivalently extends the optical path length of the local oscillator light beam L21 to compensate for the phase delay of the local oscillator light beam L22 relative to the local oscillator light beam L21 due to the difference between the optical path lengths of the local oscillator light beam L22 and the local oscillator light beam L21. After passing through the skew adjuster 33, the local oscillation light beam L21 is converged by the lens 40 to the local oscillation light beam input point of the optical hybrid 30.

The traveling direction of the other local oscillation light beam L22 is changed by 90 ° again by the reflection mirror 37, and then the other local oscillation light beam L22 travels toward the local oscillation light beam input point of the optical hybrid 31. The optical axis of the other local oscillation beam L22 reflected by the reflecting mirror 37 is located on the extension line of the optical axis of the local oscillation beam input point of the optical hybrid 31. The lens 41 is located on the optical path between the mirror 37 and the local oscillation beam input point of the optical hybrid 31 (i.e., on the extension of the optical axis of the local oscillation beam input point of the optical hybrid 31). The other local oscillation light beam L22 reflected by the mirror 37 is converged by the lens 41 to the local oscillation light beam input point of the optical hybrid 31.

As described above, the signal light beam L1 and the local oscillation light beam L2 input into the housing 2 are distributed to the two

optical mixers

30 and 31. The

optical mixers

30 and 31 are of a Photodiode (PD) integrated type using a semiconductor substrate made of, for example, indium phosphide (InP). The

optical mixers

30 and 31 cause the signal light beams L11, L12 and the local oscillator light beams L21, L22 optically coupled to the respective input points to interfere with each other, thereby extracting a signal component of the signal light beam L1 having the same phase as that of the signal component of the local oscillator light beam L2 and a signal component of the signal light beam L1 having a phase different by 90 ° from that of the signal component of the local oscillator light beam L2. Each of the preamplifiers 43 mounted in the housing 2A converts a photocurrent generated by the PD integrated in each of the

optical mixers

30, 31 into a voltage signal, and outputs from any one of the plurality of lead terminals 3.

A method of manufacturing the optical receiver module 1 having the above-described structure will be described with reference to fig. 9 to 12. Fig. 9 is an example of a flowchart showing a method of manufacturing the optical receiver module 1. Each of fig. 10, 11, and 12 is a diagram illustrating a manufacturing process of the optical receiver module 1. As shown in fig. 10, after mounting various optical components to the housing 2, the optical plug 20, the alignment sleeve 17, the first lens holder 14 holding the first optical element 11, and the

assembly tools

50, 51 are prepared (step P1).

Next, the positions of the first lens holder 14 and the optical plug 20 are adjusted using the

assembly tools

50 and 51, respectively (step P2). Step P2 includes the following steps. First, the first lens holder 14 is positioned between the bush 2b and the optical plug 20. In other words, the first optical element 11 is positioned between the bush 2b and the optical fiber unit 21. Next, the position of the first lens holder 14 is adjusted while gripping the thick cylinder 14c of the first lens holder 14 with the assembly tool 50. At this time, the position in the circumferential direction of the V-shaped notch 14d of the first lens holder 14 is made to coincide with the position in the circumferential direction of the V-shaped notch 2c of the bush 2b when viewed from the Z direction (refer to fig. 8). Then, the rear end 14a of the first lens holder 14 is pressed against the bush 2 b. Next, the optical plug 20 is positioned to face the first lens holder 14 in the Z direction while gripping the ferrule 24 with the assembly tool 51. Then, the optical plug 20 is inserted into the alignment sleeve 17, and the position of the optical plug 20 is adjusted.

Next, XYZ alignment of the PMF 23 and XY alignment of the first lens 11a are simultaneously performed (step P3). In step P3, the local oscillation light beam L2 is introduced from the PMF 23 into the housing 2, and the intensity of the local oscillation light beam L2 is detected by the built-in PDs of the

optical mixers

30 and 31. At this time, the positions of the PMF 23 and the first lens 11a are determined with reference to the intensity of the local oscillation light beam L2 detected by the built-in PD. Subsequently, XY alignment of the PMF 23 is performed while rotating the optical plug 20 with the assembly tool 51 (step P4). At this time, the rotation angle around the central axis of the PMF 23 is set to a predetermined angle so that the slow axis (slow axis) of the local oscillation light beam L2 coincides with the polarization direction of the polarizer 38. Then, the position of the PMF 23 is adjusted to maximize the optical coupling efficiency of the local oscillation light beam L2 with respect to the local oscillation light beam input points of the

optical mixers

30 and 31.

Subsequently, a wavelength sweep is performed on the local oscillation light beam L2 output from the PMF 23 (wavelengthsweeping), thereby evaluating a change in optical coupling efficiency between the PMF 23 and the optical mixers 30, 31 (step P5). As a result, if the variation in optical coupling efficiency is large, step P4 is repeated again, and PMF 23 is aligned to reduce the variation in optical coupling efficiency. If the variation in optical coupling efficiency is small, the optical plug 20 and the alignment sleeve 17 are fixed to each other by penetration type welding (step P6). Then, XY alignment of the PMF 23 is performed again, and then the first lens holder 14 and the alignment sleeve 17 are fixed to each other by welding (step P7). As a result, the first optical element 11 and the optical fiber unit 21 are fixed to each other.

Subsequently, as shown in fig. 11, the coupling sleeve 16 and the second lens holder 15 holding the second optical element 12 are prepared (step P8). Next, the intermediate assembly 1A composed of the optical plug 20, the alignment sleeve 17, and the first lens holder 14 is separated from the assembly tool 50, and the intermediate assembly 1A is lifted in the Z direction by the assembly tool 51. Next, the position of the second lens holder 15 is adjusted with the assembly tool 50 (step P9). In step P9, first, the second lens holder 15 is positioned between the first lens holder 14 and the bush 2 b. In other words, the second optical element 12 is positioned between the first optical element 11 and the bushing 2 b. Next, the thick tube 15c of the second lens holder 15 is gripped by the assembly tool 50, and the position of the second lens holder 15 is adjusted using the assembly tool 50. At this time, the position in the circumferential direction of the V-shaped notch 15d of the second lens holder 15 is made to coincide with the position in the circumferential direction of the V-shaped notch 2c of the bush 2b when viewed from the Z direction (refer to fig. 8). Then, the rear end 15a of the second lens holder 15 is pressed against the bush 2 b.

Subsequently, the first lens holder 14 is inserted into the coupling sleeve 16, and the coupling sleeve 16 is brought into contact with the front end 15b of the second lens holder 15. Next, XYZ alignment of the intermediate assembly 1A and XY alignment of the second lens 12a are simultaneously performed (step P10). In step P10, the signal light beam L1 is introduced from the SMF 22 into the case 2, and the intensity of the signal light beam L1 is detected by the built-in PD of each of the

optical mixers

30, 31. Then, the position of each of the SMF 22 and the second optical element 12 is determined with reference to the intensity of the signal light beam L1 detected by the built-in PD. Next, the second lens holder 15 and the bush 2b are fixed to each other by welding (step P11). As a result, the second optical element 12, the first optical element 11, and the bush 2b are fixed to each other. Next, the coupling sleeve 16 and the first lens holder 14 are fixed to each other by penetration type welding (step P12). Then, XY alignment of the intermediate assembly 1A is performed with the assembly tool 51, and the coupling sleeve 16 and the second lens holder 15 are fixed to each other by welding (step P13).

Next, the positions of the optical plug 20 and the first lens holder 14 are finely adjusted while the signal light beam L1 and the local oscillation light beam L2 are again introduced into the housing 2. First, as shown in fig. 12, the local oscillation light beam L2 is introduced into the housing 2 from the PMF 23 again, and the alignment sleeve 17 and the optical plug 20 are fixed to each other by forge welding (step P14) with reference to the intensity of the local oscillation light beam L2 detected by the built-in PDs of the

optical hybrids

30 and 31. Next, the signal beam L1 is introduced into the housing 2 from the SMF 22 again, and the coupling sleeve 16 and the first lens holder 14 are fixed to each other by forge welding with reference to the intensity of the signal beam L1 detected by the built-in PDs of the optical mixers 30 and 31 (step P15).

Effects obtained by the optical receiver module 1 and the manufacturing method thereof according to the above-described embodiments and problems of the conventional art will be described. As an optical transceiver using a digital coherent light transmission technology, an optical transceiver conforming to a CFP (form factor pluggable) standard is widely used. In recent years, there has been a great demand for smaller CFP2 optical transceivers. In the future, it is expected that the transition will be made from CFP2 optical transceivers to smaller CFP4 optical transceivers. With this shift, miniaturization of equipment such as modulators, wavelength tunable light sources, and optical receiver modules to be mounted in such optical transceivers is being advanced. In the optical receiver module, by causing the local oscillation beam to interfere with the signal beam that has been phase-modulated, information included in the signal beam is recovered, and a signal port for inputting the signal beam and a local oscillation port for inputting the local oscillation beam are required, for example. The signal port and the local oscillator port are connected to an SMF and a PMF (hereinafter collectively referred to as "optical fibers"), respectively.

As a technique for miniaturizing such an optical receiver module, a structure in which an optical fiber is drawn into a housing is conceivable. For example, if the optical hybrid is formed of a silica-based planar waveguide, a technique of integrally coupling the optical hybrid with an optical fiber by a butt-joint (butt-join) method may be considered. In the case where the optical hybrid is made of a semiconductor such as silicon or InP, since there is a large difference in MFD (mode field diameter) between the optical hybrid and the optical fiber, it is conceivable to adopt a butt-bonding method and use a technique such as a spot-size converter. In this case, it is more common to apply a technique of optically coupling the optical hybrid to the optical fiber using a grating coupler.

However, if the optical fiber is pulled into the housing in this way, the productivity of the light receiving module is lowered, and the optical fiber requires special handling, which may increase the cost. Therefore, it is desirable to miniaturize the optical receiver module by not adopting a structure in which the optical fiber is pulled into the housing. Therefore, as a structure in which the optical fiber is not drawn into the housing, for example, a structure in which one optical coupling system is formed by the optical fiber array and the lens array outside the housing can be considered. However, the interval between the optical axes of the lenses of the lens array and the interval between the cores of the optical fiber array easily deviate from each other due to, for example, manufacturing variability. As a result, the coupling efficiency between the fiber array and the optical hybrid inside the housing may be reduced. An optical receiver module having such a structure will be described as a comparative example.

Fig. 13 is a schematic diagram showing the configuration of an optical receiver module 100 as a comparative example. The optical receiver module 100 includes a housing 101, an optical fiber unit 110, and an array lens 120. The optical fiber unit 110 is located outside the housing 101. The optical fiber unit 110 has an SMF 111 for inputting the signal beam L1 and a PMF 112 for inputting the local oscillator beam L2. The SMF 111 and the PMF 112 input the signal beam L1 and the local oscillation beam L2 into the casing 101, respectively. The array lens 120 is located between the housing 101 and the optical fiber unit 110. The array lens 120 has

lenses

121 and 122 arranged to face the SMF 111 and the PMF 112, respectively. The optical axis B1 of the lens 121 is located at a position deviated from the extension line of the optical axis of the SMF 111, and the optical axis B2 of the lens 122 is located on the extension line of the optical axis of the PMF 112. In other words, the interval between the optical axes of the array lenses 120 and the interval between the cores of the optical fiber units 110 are different from each other. The lens 121 converts the signal light beam L1 output from the SMF 111 into collimated light. The lens 122 converts the local oscillation light beam L2 output from the PMF 112 into collimated light.

The light mixer 130,

lenses

131, 132 and preamplifier 133 are located in the housing 101. The lens 131 is located between the signal beam input point of the optical hybrid 130 and the lens 121. The lens 132 is located between the local oscillator beam input point of the optical hybrid 130 and the lens 122. The preamplifier 133 converts a photocurrent generated by the PD integrated in the optical hybrid 130 into a voltage signal. Then, the voltage signal is output from any one of the plurality of lead terminals 134 mounted in the case 101.

In the optical receiver module 100 having the above-described configuration, the local oscillation light beam L2 output from the PMF 112 directly passes through the lens 122, and is then converged by the lens 132 to the local oscillation light beam input point of the optical hybrid 130. On the other hand, when the signal light beam L1 output from the SMF 111 enters the lens 121, the signal light beam L1 is bent within the lens 121 with respect to the optical axis B1 of the lens 121. Then, the signal light beam L1 is output from the lens 121 and enters the lens 131 in a state of being inclined with respect to the optical axis of the lens 131. Therefore, if the signal light beam L1 enters the lens 131 in a state of being inclined with respect to the optical axis of the lens 131, the position at which the signal light beam L1 is converged by the lens 131 deviates from the position of the signal light beam input point of the optical hybrid 130. As a result, a problem arises in that the coupling efficiency between the SMF 111 and the optical hybrid 130 is reduced.

In contrast, in the optical receiver module 1 of the present embodiment, as shown in fig. 2, the first optical element 11 having the first lens 11a located on the optical path of the local oscillator light beam L2 and the second optical element 12 having the second lens 12a located on the optical path of the signal light beam L1 are disposed side by side in the Z direction, the first optical element 11 transmits the signal light beam L1 and the local oscillator light beam L2, and the second optical element 12 transmits the signal light beam L1 and the local oscillator light beam L2. Therefore, the interval between the optical axis a1 of the first lens 11a and the optical axis a2 of the second lens 12a can be narrowed (refer to fig. 3), and one optical coupling system including the first lens 11a and the second lens 12a for the optical fiber unit 21 can be constituted. In other words, the first lens 11a and the second lens 12a may be received in a single coupling portion 10. As a result, the size of the optical receiver module 1 can be reduced. Further, the first lens 11a and the second lens 12a are individually provided in the first optical element 11 and the second optical element 12, respectively. In other words, the first lens 11a and the second lens 12a are not integrated into a single unit. Therefore, in manufacturing the optical receiver module 1, the first lens 11a and the second lens 12a can be aligned separately. As a result, a decrease in optical coupling efficiency between the PMF 23 and the first optical component and a decrease in optical coupling efficiency between the SMF 22 and the second optical component can be reduced.

The optical axis a1 of the first lens 11a and the optical axis a2 of the second lens 12a are located at positions deviated from the center C1 of the first optical element 11 and the center C2 of the second optical element 12, respectively. The planar region 11e of the first optical element 11 has no lens and is located on an extension of the optical axis a2 of the second lens 12a, and the planar region 12e of the second optical element 12 has no lens and is located on an extension of the optical axis a1 of the first lens 11a (refer to fig. 3). Therefore, the alignment of the first lens 11a can be performed without being affected by the position of the second optical element 12, and the alignment of the second lens 12a can be performed without being affected by the position of the first optical element 11. As a result, a decrease in optical coupling efficiency between the PMF 23 and the first optical component and a decrease in optical coupling efficiency between the SMF 22 and the second optical component can be reduced.

The first optical element 11 is located between the optical fiber unit 21 and the second optical element 12. The method of manufacturing the optical receiver module 1 includes: steps P2 and P3 of positioning the first optical element 11 between the one end surface 2a and the optical fiber unit 21 and aligning the first lens 11a of the first optical element 11; a step P7 of fixing the first optical element 11 and the optical fiber unit 21 to each other; steps P9 and P10 of positioning the second optical element 12 between the one end surface 2a and the first optical element 11 and aligning the second lens 12a of the second optical element 12; and a step P11 of fixing the second optical element 12, the first optical element 11, and the one end surface 2a to each other. In manufacturing the optical receiver module 1, it is desirable to align the second lens 12a after aligning the first lens 11a and fixing the position of the first optical element 11. The reason is as follows. In aligning the first lens 11a, it is necessary to rotate the optical fiber unit 21 about the central axis in order to adjust the polarization direction of the local oscillation light beam L2. If the second lens 12a is first aligned and fixed to the optical fiber unit 21, when the optical fiber unit 21 is rotated about the central axis to then align the first lens 11a, the position of the second lens 12a moves about the central axis with the rotation. As a result, the position of the optical axis of the aligned second lens 12a may deviate. Therefore, positioning the first optical element 11 between the optical fiber unit 21 and the second optical element 12 makes it possible to align the first lens 11a first and reduce deviation of the optical axis position of the second lens 12a due to the influence of the alignment of the first lens 11 a. As a result, the decrease in the optical coupling efficiency between the SMF 22 and the second optical component can be further reduced.

The second lens 12a is a meniscus lens. Therefore, even if the distance between the second lens 12a and the optical fiber unit 21 is longer than the distance between the first lens 11a and the optical fiber unit 21 in the Z direction, the size of the beam diameter of the signal beam L1 transmitted through the second lens 12a can be made close to the size of the beam diameter of the local oscillator beam L2 transmitted through the first lens 11 a. As a result, the decrease in the optical coupling efficiency between the SMF 22 and the second optical component can be further reduced.

One end surface 2a is provided on a bush 2b, the bush 2b is positioned on a side wall with a window of the housing 2 and has a V-shaped notch 2c on the outer periphery of the bush 2b, and the V-shaped notch 14d, the V-shaped notch 15d, and the V-shaped notch 2c are located on a line parallel to the Z direction.

(modification example)

Fig. 14 is a front view showing the first lens holder 14A according to a modification of the above-described embodiment. Fig. 15 is a side view showing the first lens holder 14A according to the modification. Fig. 16 is a front view showing the second lens holder 15A according to the modification. Fig. 17 is a side view showing the second lens holder 15A according to the modification. Fig. 14 and 16 are views of the first lens holder 14A and the second lens holder 15A, respectively, when viewed from the Z direction, and fig. 15 and 17 are views of the first lens holder 14A and the second lens holder 15A, respectively, when viewed from the Y direction. Fig. 18 is a side view showing a state where the first lens holder 14A, the second lens holder 15A, the coupling sleeve 16, and the alignment sleeve 17 are assembled together, and the rear end 15A of the second lens holder 15A is engaged with the bush 2 b. Fig. 18 is a diagram when viewed from the Y direction.

The difference between this modification and the above-described embodiment is the shape of the first lens holder 14A, the shape of the second lens holder 15A, and the shape of the bush 2b in the modification. Specifically, the first lens holder 14A includes an indication plane 14f instead of the V-shaped cutout 14d, the second lens holder 15A includes an indication plane 15f instead of the V-shaped cutout 15d, and the bush 2b includes an indication plane 2d instead of the V-shaped cutout 2 c. Each of the indicating plane 2d, the indicating plane 14f, and the indicating plane 15f is chamfered (chamfer) in the XZ plane. In other words, each of the indicating plane 2d, the indicating plane 14f, and the indicating plane 15f is a flat surface along the XZ plane. The relative position of the first lens 11a with respect to the first lens holder 14 is defined by defining the relative angle of the first optical element 11 with respect to the first lens holder 14 about its central axis with reference to the position of the indication plane 14 f. Further, by defining the relative angle of the second optical element 12 about its central axis with respect to the second lens holder 15 with reference to the position of the indication plane 15f, the relative position of the second lens 12a with respect to the second lens holder 15 is defined.

As shown in fig. 18, each of the indication plane 14f and the indication plane 15f is located at the same position in the circumferential direction as the indication plane 2d formed on the outer circumferential surface of the bush 2 b. In other words, each of the indicating plane 14f, the indicating plane 15f, and the indicating plane 2d is located on a line parallel to the Z direction. The shape of the indicating plane 14f and the shape of the indicating plane 15f coincide with the shape of the indicating plane 2d in the circumferential direction. By making the position in the circumferential direction of the indication plane 14f of the first lens holder 14 coincide with the position in the circumferential direction of the indication plane 2d of the bush 2b, the relative angle of the first lens holder 14 with respect to the bush 2b about the central axis thereof is defined. Thereby, the relative position of the first lens 11a with respect to the bushing 2b is defined. By making the position in the circumferential direction of the indication plane 15f of the second lens holder 15 coincide with the position in the circumferential direction of the indication plane 2d of the bush 2b, the relative angle of the second lens holder 15 with respect to the bush 2b about the central axis thereof is defined. Thereby, the relative position of the second lens 12a with respect to the bushing 2b is defined.

The coherent optical receiver module and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment and modification, the first lens 11a is formed on the front end surface 11b of the first optical element 11, but the first lens 11a may be formed on both the front end surface 11b and the rear end surface 11c of the first optical element.

The present application is based on and claims priority of japanese patent application No.2017-138156 filed on 14.7.2017; the entire contents of this japanese patent application are incorporated herein by reference.

Claims

1. A coherent optical receiver module for demodulating information contained in a signal optical beam by interfering a local oscillator optical beam with the phase-modulated signal optical beam, comprising:

a housing having one end surface intersecting a first direction, the housing accommodating therein a first optical component arranged on an optical path of the local oscillation beam and a second optical component arranged on an optical path of the signal beam;

an optical fiber set disposed facing the end surface, the optical fiber set including a first optical fiber optically coupled with the first optical component to propagate the local oscillator beam and a second optical fiber optically coupled with the second optical component to propagate the signal beam;

A first optical element having a first lens disposed on an optical path of the local oscillation beam output from the first optical fiber, the first optical element being configured to transmit the signal beam and the local oscillation beam; and

a second optical element having a second lens disposed on an optical path of the signal beam output from the second optical fiber, the second optical element being configured to transmit the signal beam and the local oscillation beam therethrough,

wherein the first optical element and the second optical element are placed side by side along the first direction between the optical fiber group and the one end surface,

wherein the first lens and the second lens are arranged such that an optical axis of the first lens and an optical axis of the second lens are not aligned with a center of the first optical element and a center of the second optical element,

wherein a first region of the first optical element opposite to the first lens with respect to a center of the first optical element has no lens and is located on an extension of an optical axis of the second lens.

2. The coherent optical receiver module of claim 1,

wherein a second region of the second optical element opposite to the second lens with respect to a center of the second optical element has no lens and is located on an extension of an optical axis of the first lens.

3. The coherent optical receiver module of claim 1,

wherein a first region of the first optical element opposite to the first lens with respect to a center of the first optical element defines a planar region and is located on an extension of an optical axis of the second lens.

4. The coherent optical receiver module of claim 1,

wherein a second region of the second optical element opposite to the second lens with respect to a center of the second optical element defines a planar region and is located on an extension of an optical axis of the first lens.

5. The coherent optical receiver module of claim 1,

wherein the first optical element is located between the group of optical fibers and the second optical element in the first direction.

6. The coherent optical receiver module of claim 1,

wherein the second lens comprises a meniscus lens.

7. The coherent optical receiver module of claim 1,

wherein the second optical element includes a surface facing the end surface of the housing, the surface of the second optical element being provided with a concave surface of the second lens.

8. The coherent optical receiver module of any one of claims 1 to 7, further comprising a first holder holding the first optical element and a second holder holding the second optical element.

9. The coherent optical receiver module of claim 8,

wherein the housing comprises a bushing arranged adjacent to a side wall of the housing having a window and provided with the end surface, and

the first holder has a first positioning portion on an outer periphery, the second holder has a second positioning portion on an outer periphery, and the bush has a third positioning portion on an outer periphery, and the first positioning portion, the second positioning portion, and the third positioning portion are aligned on a line parallel to the first direction.

10. The coherent optical receiver module of claim 8,

wherein the first holder comprises a cut-out or an indication plane on the outer circumference and the second holder comprises a cut-out or an indication plane on the outer circumference, and

the cutout or indicating plane of the first holder is aligned with the cutout or indicating plane of the second holder.

11. The coherent optical receiver module of claim 10,

Wherein the housing comprises a bushing arranged adjacent to a side wall of the housing with a window and provided with the end surface, and the bushing comprises a cut-out or an indication plane on the outer circumference, and

the cut-out or indicating plane of the first holder, the cut-out or indicating plane of the second holder and the cut-out or indicating plane of the bush are aligned on a line parallel to the first direction.

12. A method of manufacturing a coherent optical receiver module, comprising:

preparing a housing having one end surface, an optical fiber group including a first optical fiber configured to propagate a local oscillator beam and a second optical fiber configured to propagate a signal beam, a first optical element having a first lens, and a second optical element having a second lens;

positioning the first optical element between the end surface of the housing and the set of optical fibers to align the first lens of the first optical element with an optical axis of the first optical fiber;

securing the first optical element to the group of optical fibers;

positioning the second optical element between the end surface and the first optical element to align the second lens of the second optical element with an optical axis of the second optical fiber; and

Fixing the second optical element to the first optical element and the end surface of the housing,

13. The method of manufacturing a coherent optical receiver module of claim 12,

wherein in the preparation, a first holder holding the first optical element therein is prepared together with the first optical element, and a second holder holding the second optical element therein is prepared together with the second optical element,

the housing is provided with a bush adjacent to a side wall of the housing, and the first and second holders and the bush each have a cut-out or an indication plane,

in the step of positioning the first optical element, the cut or indication plane of the first holder is aligned with the cut or indication plane of the bush, and

In the step of positioning the second optical element, the cut or indicating plane of the second holder is aligned with the cut or indicating plane of the bush.